DN Join Rules

A DN join rule determines the DN of entries in the secondary data
view. A DN join rule is configured on the secondary data view by using the dn-join-rule property. Only one DN join rule can be configured on
a secondary data view. If a DN join rule is configured on a data view, a filter
join rule cannot be configured on that data view.

A DN join rule has DN syntax and can take one of the following forms:

The DN of the secondary entry is constructed from an attribute
in the primary entry.

For example, the following DN join rule
stipulates that the DNs of entries in the secondary data view should include
the cn from the primary data view, plus the ou=people suffix.

cn=\${primary-data-view.cn},ou=people

The DN must not contain the base DN of the secondary
data view. In this sense, it is a relative DN.

The DN of the secondary entry is the same as the DN of the
primary entry.

The syntax of such a join rule is as follows:

\${primary-data-view.dn}

In this case, the portion of the primary and the secondary DNs below
the base DN are identical, although the full DNs may differ. Imagine, for
example, that the primary data view has a base DN of o=primary and
the secondary data views has a base DN of o=secondary.
A join rule of \${primary-data-view.dn} implies
that the DITs below the base DN are identical. So, the entry uid=1,o=secondary would be associated with uid=1,o=primary.